Paul,
The negative kappa is an indication that the degree of agreement is less
than would be expected by chance. What you've run into is the paradox that
occurs with kappa and most kappa-like statistics that Feinstein and Cichetti
first mentioned. As marginal homogeneity decreases (trait prevalence
becomes more skewed), the value of kappa decreases in spite of the fact that
rater agreement might be very high. Scott's pi, Cohen's kappa, and Conger's
kappa were all developed based on the assumption of marginal homogeneity.
The greater the deviation, the more kappa is diminished. This is one of the
criticisms of kappa type statistics. Regarding your second question, use the
kappa value of -0.0345. The 0.1155 is the asymptotic standard error for use
in computing confidence intervals.
Brian
Brian G. Dates, Director of Quality Assurance
Southwest Counseling and Development Services
1700 Waterman
Detroit, Michigan 48209
Telephone: 313.841.7442
FAX: 313.841.4470
email:
[hidden email]
> -----Original Message-----
> From: Paul Mcgeoghan [SMTP:
[hidden email]]
> Sent: Thursday, November 09, 2006 11:33 AM
> To:
[hidden email]
> Subject: Cohen's Kappa for multiple raters
>
> Hi,
>
> I am using the syntax below from Raynald's SPSS Tools website:
>
http://www.spsstools.net/Syntax/Matrix/CohensKappa.txt>
> In my case I have 6 raters rating 5 subjects and there are 2 categories so
> the data is as below:
>
> Subj rater1 rater2 rater3 rater4 rater5
> rater6
> 1 2 2 2 2
> 2 2
> 2 2 2 2 2
> 2 2
> 3 2 2 2 2
> 2 2
> 4 1 2 2 2
> 2 2
> 5 2 2 2 2
> 2 2
>
> This gives a value of -.0345 which indicates no agreement according to the
> following article:
>
http://en.wikipedia.org/wiki/Fleiss%27_kappa>
> Most of the raters agree in the above table so why is Cohen's Kappa
> negative, indicating no
> agreement.
>
> Also in the output, it gives Cohen's Kappa where Kappa is -.0345 and
> Cohen's Kappa Fleiss - adjusted standard error as .1155
>
> Which value do I use for Cohen's Kappa among multiple raters, is it -.0345
> or .1155?
>
> Paul
>
>
> ==================
> Paul McGeoghan,
> Application support specialist (Statistics and Databases),
> University Infrastructure Group (UIG),
> Information Services,
> Cardiff University.
> Tel. 02920 (875035).
>
>
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